1. Field of the Invention
This invention relates to video recording and/or reproducing apparatus, and is more particularly directed to video tape apparatus whereby editing of a video signal may be carried out.
2. Brief Description of the Prior Art
Conventional video tape recorders (VTRs), of the type having one or more rotating heads which scan the video tape at an angle to the direction of advancement thereof, can be adapted to be set into editing modes so that a new scene is recorded continuously after a previously recorded scene. In one much mode, sometimes called an assemble mode, after one scene is recorded, the VTR is stopped, following which another scene is recorded immediately thereafter. In another mode, sometimes called an insert mode, a new scene is recorded between two scenes which were recorded previously on the tape.
In either the insert or assemble mode, the edit points, i.e., the points connecting the respective successive scenes, are determined, for example, by an operator viewing the video picture on a monitor. In a usual edit operation, the operator stops the VTR at a selected point by depressing a pause button. Then, when the operator is ready to record the new video material, the VTR is released from its pause mode and is set into its record mode, and a new video scene is recorded beginning at the edit point.
Whenever such assemble or insert recording operations are performed, care must be taken to prevent the video signal from generating confusion or noise at the edit point. For this reason, at the edit point the pitch of the recording head traces should correspond to the pitch of the tracks previously recorded on the tape. If the pitch of the recorded tracks changes discontinuously at the edit point, the reproduction of the recorded signals in the tracks around the edit point will become degraded. More particularly, when the track pitch changes, the reproducing heads will not accurately scan the recorded signal, and the reproduced picture will become noisy. Also, when the track pitch changes, the reproduced vertical and horizontal synchronizing signals will occur at a time that does not correspond to previously picked up synchronizing signals, and synchronization of the reproduced video will become unreliable.
In order to avoid changes in the track pitch at an edit point, conventional techniques take advantage of a control track recorded at one edge of the video tape, and recognize that the positions of the video tracks correspond accurately to positions of the control signal recorded on the tape. That is, in the recorded signal after editing, the pulses of the control signal have a constant pitch .tau..sub.c.
In order to avoid changes in track pitch, the recording of the tracks of the new video signal should be controlled by the tracking servo system of the VTR, so that the tracks are recorded at locations determined by the recorded control signal corresponding to a previously-recorded scene, while the recording heads are rotated in synchronism with the vertical synchronism with the vertical synchronizing signal contained in the new video signal.
To carry out recording under the control of the tracking servo system, the tape must be reversed for at least a short distance adhead of the edit point. Then, the new scene is recorded, beginning at the edit point, only after the tape has been advanced for that short distance. Thus, the track pitch for the new video signal matches that of the previously recorded video signal, and picture degradation or synchronization confusion is avoided at the edit point.
According to conventional editing techniques, the tape is returned for a short distance to reverse it for the above-mentioned short distance.
The tape is stopped after predetermined amount of tape is returned. Then, when it is desired to record the new scene, the advancement of the tape is commenced immedaitely prior to the recording of the new scene for synchronization of the tracking servo system. However, when the tape is re-started in the forward direction by releasing the pause button, the tracking servo circuit cannot be locked-in immediately after the restarting thereof.
In other words, if the servo circuit has an ideal rising characteristic relative to tape transportation as shown by a straight broken line a in FIG. 1, the servo circuit is immediately locked in at the time when a first control pulse CTL.sub.1 and a first RF switching pulse P.sub.1 are coincident with one-other. However, the servo circuit doesn't have such a quick response, the servo circuit enters into the lock-in condition after quite a long time passes. Now assuming that the rising characteristic of the servo circuit is poor as shown by one-dot dash line b in FIG. 1, the servo circuit is indicated to be locked-in at the time when a fourth control signal CTL.sub.4 and a sixth RF switching pulse P.sub.6 are coincident with one other.
This means that a conventional editing system has the disadvantage that it takes a relatively long time for the servo circuit to fall into the lock-in condition.
On the other hand, in the above-described type of the editing system, it is frequently required to confirm or monitor a recording condition or the recorded contents of the previously recorded video signal.
However, the conventional editing system has another disadvantage in that the system is not provided with a monitoring function which prevents the shift of the edit point.